Some internal combustion engines for vehicles provide a throttle valve at the upstream side of intake manifolds (air intake passages), and provide a fuel injection valve and an air flow rate sensor at the downstream side of the throttle valve (for example, refer to Japanese Examined Patent Application, Second Publication No. H04-15388). An intake air volume signal which is an output from the air flow rate sensor is input to a control circuit, and a fuel injection quantity is calculated in response to the operational state of the internal combustion engine. In addition, an injection quantity signal based on the calculated fuel injection quantity is output from a control circuit to control the operation of the fuel injection valve.
Internal combustion engines for racing cars and motorcycles, for which a fast-response to the throttle operation is considered to be important, do not use intake manifolds but provide an individual air intake passage for each cylinder. Each air intake passage provides a throttle body. In this case, when throttle valve openings are small, fuel injection is performed based on an output from a pressure sensor provided on each air intake passage and the engine speed; and when the throttle valve openings are large, fuel injection is performed directly in response to the opening and the engine speed.
However, providing a pressure sensor for each cylinder increases the number of components, increasing the cost. Also, determining fuel injection quantity based only on the openings and the engine speed when the throttle valve openings are large has disadvantages in fuel consumption and in reduction of exhaust gas.
The present invention has been realized in view of the above-stated situations and has an object to provide an air intake apparatus and a control apparatus for an internal combustion engine providing an air intake passage and a throttle body for each cylinder, with a fast response and optimum fuel injection, with a small number of components.